The phosphorylation of nuclear proteins is a prominent cellular response to polypeptide hormones. The physiological relevance of this response remains to be established. One of the nuclear proteins showing marked hormone-dependent phosphorylation is histone H1. This protein plays an important role in causing the nucleosomal "string of beads" to condense into a more compact structure. We propose to study the role that TSH plays in the regulation of nucleosomal protein phosphorylation in the thyroid. In vitro studies will be performed on various classes of oligonucleosomes with nuclear and cytoplasmic protein kinases. The patterns of phosphorylation that are obtained in these in vitro studies will be compared with those observed following TSH and other hormonal stimulation of thyroid slices in vivo. The degree of H1 phosphorylation and the distribution of nucleosomes in various size-classes will be studied following hormonal stimulation in vivo. Similar studies will be performed on non-histone nuclear proteins which show hormonal stimulation. These studies should help to establish a physiological basis for the hormone-dependent phosphorylation of specific nuclear proteins, a wide-spread and striking effect of polypeptide hormones on their target organs, which may play a role in the regulation of genetic expression in such cells.